Description of a Nciv Plesiosaur. 



319 



und slightly convex facet ; its anterior border is sharp and almost 

 straight, while the post-axial border is concave in its proximal half 

 but distally is occupied by a large facet for union with the fibula, 

 with which there seems to have been no contact at the proximal 

 end. Distally there is a long, flat facet for the tibiale ; in front of 

 this there is a small, oblique facet and behind it a longer, also oblique 

 facet for the intermedium. The fibula (fib.) is a kidney-shaped 

 bone ; proximally it bears a large, nearly straight surface for union 

 with the femur ; anteriorly it has in its proximal portion a concave, 



FIG. 4. 



4. Portion of hind paddle of Plesioxaurus ca2)e>isis. About ^ nat. size. 

 fern., femur; fib., fibula ; till., tibia. 



sharp-edged border and distally a facet for union with the tibia. 

 The remainder of the border is occupied by four facets one for 

 the intermedium, behind this a surface for the fibulare, next a post- 

 axial surface looking nearly directly backwards, and lastly a small 

 surface looking upwards and backwards, which probably supported 

 an accessory ossicle which also articulated with the femur. The 

 chief peculiarity of this tibia and fibula, apart from their length, is 

 that, although they unite distally, proximally there is a considerable 

 interval between them which is only closed above by the humerus. 

 I am not acquainted with any Plesiosaur in which exactly the same 

 thing is seen ; usually in the post-Liassic Plesiosaurs the tibise and 



